The invention relates to the manner in which an electrical lead which extends over the length of a carbon brush is attached to the brush.
In a conventional carbon brush known from German utility model 8,716,985 the connecting lead is formed as a strip of woven metal fabric or metal foil which is secured to the brush by mechanically clamping it in a dovetailed recess of the brush. The lead is mechanically and electrically connected to the carbon brush, in part by clamping it in the recess, and in part by a galvanically applied metal layer which overlays the lead. However, the strength of the connection between the lead and the brush is dependent on production tolerances. These may fluctuate over the length of the brush, thus rendering it difficult to obtain precise values for the strength of the mechanical connection and the resistance of the electrical connection.
German patent publication DE-OS 34 05 674 discloses a carbon brush which has a metallic plating that coats the underside or a groove in the underside of the brush. The lead, in the form of a strip of woven metallic fabric or a metal foil, is soldered to the plating on the underside of the brush. Soldering involves, however, an additional manufacturing step. Moreover, the soldering temperature produces stresses between the metallic layer and the underside of the carbon brush as a result of differing rates of thermal expansion. This can lead to a separation of the metallic layer.